White Light Induced
E/Z-Photoisomerization of Diphenylamine-Tethered
Fluorescent Stilbene Derivatives: Synthesis, Photophysical, and Electrochemical
Investigation
A facile synthesis
and detailed photophysical investigation of
E/Z-isomerization of fluorescent diphenylamine tethered stilbene derivatives
(DPASs) under white light exposure have been carried out to understand
the effect on fluorescence, electrochemical properties, and photostability
under various activation/deactivation pathways. In solution state,
in the dark, the E-isomer of DPASs (6a–d) exhibited high fluorescence quantum yields (Φfl ≈ 53% to 60% in DMSO). However, on white light exposure, 1H NMR and HPLC studies revealed that pure E-isomer of the
DPAS 6a (∼9.5 mM) started converting into its
Z-form by photoisomerization until it reaches to nearly equilibrium.
At low concentrations (∼10 μM), the absorption band of
the pure E-isomer in the range of 350–450 nm gradually decreased
to adopt Z-conformation 6a′ until a photostationary
state was reached. The structure of the E-isomer 6a was
unequivocally confirmed by X-ray diffraction analysis. The synthesized
DPAS compounds 6a–d possessed positive
solvatochromic properties, two photon absorption properties, and good
thermal stability. The electrochemical investigations using DPASs
showed reversible oxidation resulting in formation of a stable radical
cation. Owing to useful photophysical, electrochemical and thermal
properties, these DPAS derivatives are suitable for their application
in biomedical imaging as well as in fabrication of electroluminescent
materials.